Subtractive Inhibition Research Articles

Long-range GABAergic projections contribute to cortical feedback control of sensory processing

In the olfactory system, the olfactory cortex sends glutamatergic projections back to the first stage of olfactory processing, the olfactory bulb (OB). Such corticofugal excitatory circuits — a canonical circuit motif described in all sensory systems— dynamically adjust early sensory processing. Here, we uncover a corticofugal inhibitory feedback to OB, originating from a subpopulation of GABAergic neurons in the anterior olfactory cortex and innervating both local and output OB neurons. In vivo imaging and network modeling showed that optogenetic activation of cortical GABAergic projections drives a net subtractive inhibition of both spontaneous and odor-evoked activity in local as well as output neurons. In output neurons, stimulation of cortical GABAergic feedback enhances separation of population odor responses in tufted cells, but not mitral cells. Targeted pharmacogenetic silencing of cortical GABAergic axon terminals impaired discrimination of similar odor mixtures. Thus, corticofugal GABAergic projections represent an additional circuit motif in cortical feedback control of sensory processing.

Subtractive inhibition assay for the detection of Campylobacter jejuni in chicken samples using surface plasmon resonance

In this work, a subtractive inhibition assay (SIA) based on surface plasmon resonance (SPR) for the rapid detection of Campylobacter jejuni was developed. For this, rabbit polyclonal antibody with specificity to C. jejuni was first mixed with C. jejuni cells and unbound antibody was subsequently separated using a sequential process of centrifugation and then detected using an immobilized goat anti-rabbit IgG polyclonal antibody on the SPR sensor chip. This SIA-SPR method showed excellent sensitivity for C. jejuni with a limit of detection (LOD) of 131 ± 4 CFU mL−1 and a 95% confidence interval from 122 to 140 CFU mL−1. The method has also high specificity. The developed method showed low cross-reactivity to bacterial pathogens such as Salmonellaenterica serovar Typhimurium (7.8%), Listeria monocytogenes (3.88%) and Escherichia coli (1.56%). The SIA-SPR method together with the culturing (plating) method was able to detect C. jejuni in the real chicken sample at less than 500 CFU mL−1, the minimum infectious dose for C. jejuni while a commercial ELISA kit was unable to detect the bacterium. Since the currently available detection tools rely on culturing methods, which take more than 48 hours to detect the bacterium, the developed method in this work has the potential to be a rapid and sensitive detection method for C. jejuni.

Light adaptation controls visual sensitivity by adjusting the speed and gain of the response to light.

The range of c. 1012 ambient light levels to which we can be exposed massively exceeds the <103 response range of neurons in the visual system, but we can see well in dim starlight and bright sunlight. This remarkable ability is achieved largely by a speeding up of the visual response as light levels increase, causing characteristic changes in our sensitivity to different rates of flicker. Here, we account for over 65 years of flicker-sensitivity measurements with an elegantly-simple, physiologically-relevant model built from first-order low-pass filters and subtractive inhibition. There are only two intensity-dependent model parameters: one adjusts the speed of the visual response by shortening the time constants of some of the filters in the direct cascade as well as those in the inhibitory stages; the other parameter adjusts the overall gain at higher light levels. After reviewing the physiological literature, we associate the variable gain and three of the variable-speed filters with biochemical processes in cone photoreceptors, and a further variable-speed filter with processes in ganglion cells. The variable-speed but fixed-strength subtractive inhibition is most likely associated with lateral connections in the retina. Additional fixed-speed filters may be more central. The model can explain the important characteristics of human flicker-sensitivity including the approximate dependences of low-frequency sensitivity on contrast (Weber’s law) and of high-frequency sensitivity on amplitude (“high-frequency linearity”), the exponential loss of high-frequency sensitivity with increasing frequency, and the logarithmic increase in temporal acuity with light level (Ferry-Porter law). In the time-domain, the model can account for several characteristics of flash sensitivity including changes in contrast sensitivity with light level (de Vries-Rose and Weber’s laws) and changes in temporal summation (Bloch’s law). The new model provides fundamental insights into the workings of the visual system and gives a simple account of many visual phenomena.

Gain control with A-type potassium current: IA as a switch between divisive and subtractive inhibition.

Neurons process and convey information by transforming barrages of synaptic inputs into spiking activity. Synaptic inhibition typically suppresses the output firing activity of a neuron, and is commonly classified as having a subtractive or divisive effect on a neuron’s output firing activity. Subtractive inhibition can narrow the range of inputs that evoke spiking activity by eliminating responses to non-preferred inputs. Divisive inhibition is a form of gain control: it modifies firing rates while preserving the range of inputs that evoke firing activity. Since these two “modes” of inhibition have distinct impacts on neural coding, it is important to understand the biophysical mechanisms that distinguish these response profiles. In this study, we use simulations and mathematical analysis of a neuron model to find the specific conditions (parameter sets) for which inhibitory inputs have subtractive or divisive effects. Significantly, we identify a novel role for the A-type Potassium current (IA). In our model, this fast-activating, slowly-inactivating outward current acts as a switch between subtractive and divisive inhibition. In particular, if IA is strong (large maximal conductance) and fast (activates on a time-scale similar to spike initiation), then inhibition has a subtractive effect on neural firing. In contrast, if IA is weak or insufficiently fast-activating, then inhibition has a divisive effect on neural firing. We explain these findings using dynamical systems methods (plane analysis and fast-slow dissection) to define how a spike threshold condition depends on synaptic inputs and IA. Our findings suggest that neurons can “self-regulate” the gain control effects of inhibition via combinations of synaptic plasticity and/or modulation of the conductance and kinetics of A-type Potassium channels. This novel role for IA would add flexibility to neurons and networks, and may relate to recent observations of divisive inhibitory effects on neurons in the nucleus of the solitary tract.

Functional MRI, ERP, and psychophysical measures show that contextual effects are orientation tuned and suppressive

The response of V1 neurons to a stimulus placed inside the classical receptive field can be modulated by stimuli presented outside the classical receptive field. However, the specific nature of these contextual modulations is unknown. Both enhancement and suppression have been observed as well as variability across measurement methodologies. To assess whether the contextual effect is facilitative or suppressive, we measured neural responses to an oriented Gabor stimulus ("target") in three conditions: in isolation, with two Gabor flankers that were the same orientation as the target, and with two flankers that were orthogonal to the target orientation. We show that the target-related fMRI response, event-related potential amplitude, and the amount of contrast adaptation are all lower when the flankers were the same orientation compared to both the isolated and orthogonal conditions. There was no evidence of response enhancement. These results all point to an orientation-tuned suppressive effect of contextual stimuli measured in the periphery that is well explained by models incorporating divisive or subtractive inhibition.

Signal integration at spherical bushy cells enhances representation of temporal structure but limits its range.

Neuronal inhibition is crucial for temporally precise and reproducible signaling in the auditory brainstem. Previously we showed that for various synthetic stimuli, spherical bushy cell (SBC) activity in the Mongolian gerbil is rendered sparser and more reliable by subtractive inhibition (Keine et al., 2016). Here, employing environmental stimuli, we demonstrate that the inhibitory gain control becomes even more effective, keeping stimulated response rates equal to spontaneous ones. However, what are the costs of this modulation? We performed dynamic stimulus reconstructions based on neural population responses for auditory nerve (ANF) input and SBC output to assess the influence of inhibition on acoustic signal representation. Compared to ANFs, reconstructions of natural stimuli based on SBC responses were temporally more precise, but the match between acoustic and represented signal decreased. Hence, for natural sounds, inhibition at SBCs plays an even stronger role in achieving sparse and reproducible neuronal activity, while compromising general signal representation.

A Neural Signature of Divisive Normalization at the Level of Multisensory Integration in Primate Cortex

Studies of multisensory integration by single neurons have traditionally emphasized empirical principles that describe nonlinear interactions between inputs from two sensory modalities. We previously proposed that many of these empirical principles could be explained by a divisive normalization mechanism operating in brain regions where multisensory integration occurs. This normalization model makes a critical diagnostic prediction: a non-preferred sensory input from one modality, which activates the neuron on its own, should suppress the response to a preferred input from another modality. We tested this prediction by recording from neurons in macaque area MSTd that integrate visual and vestibular cues regarding self-motion. We show that many MSTd neurons exhibit the diagnostic form of cross-modal suppression, whereas unisensory neurons in area MT do not. The normalization model also fits population responses better than a model based on subtractive inhibition. These findings provide strong support for a divisive normalization mechanism in multisensory integration.

Gain control through divisive inhibition prevents abrupt transition to chaos in a neural mass model.

Experimental results suggest that there are two distinct mechanisms of inhibition in cortical neuronal networks: subtractive and divisive inhibition. They modulate the input-output function of their target neurons either by increasing the input that is needed to reach maximum output or by reducing the gain and the value of maximum output itself, respectively. However, the role of these mechanisms on the dynamics of the network is poorly understood. We introduce a novel population model and numerically investigate the influence of divisive inhibition on network dynamics. Specifically, we focus on the transitions from a state of regular oscillations to a state of chaotic dynamics via period-doubling bifurcations. The model with divisive inhibition exhibits a universal transition rate to chaos (Feigenbaum behavior). In contrast, in an equivalent model without divisive inhibition, transition rates to chaos are not bounded by the universal constant (non-Feigenbaum behavior). This non-Feigenbaum behavior, when only subtractive inhibition is present, is linked to the interaction of bifurcation curves in the parameter space. Indeed, searching the parameter space showed that such interactions are impossible when divisive inhibition is included. Therefore, divisive inhibition prevents non-Feigenbaum behavior and, consequently, any abrupt transition to chaos. The results suggest that the divisive inhibition in neuronal networks could play a crucial role in keeping the states of order and chaos well separated and in preventing the onset of pathological neural dynamics.

Inhibitory Actions Unified by Network Integration

Cortical function is regulated by a strikingly diverse array of local-circuit inhibitory neurons. We evaluated how optogenetically activating somatostatin- and parvalbumin-positive interneurons subtractively or divisively suppressed auditory cortical cells' responses to tones. In both awake and anesthetized animals, we found that activating either family of interneurons produced mixtures of divisive and subtractive effects and that simultaneously recorded neurons were often suppressed in qualitatively different ways. A simple network model shows that threshold nonlinearities can interact with network activity to transform subtractive inhibition of neurons into divisive inhibition of networks, or vice versa. Varying threshold and the strength of suppression of a model neuron could determine whether the effect of inhibition appeared divisive, subtractive, or both. We conclude that the characteristics of response inhibition specific to a single interneuron type can be "masked" by the network configuration and cellular properties of the network in which they are embedded.

A novel and highly specific phage endolysin cell wall binding domain for detection of Bacillus cereus.

Rapid, specific and sensitive detection of pathogenic bacteria is crucial for public health and safety. Bacillus cereus is harmful as it causes foodborne illness and a number of systemic and local infections. We report a novel phage endolysin cell wall-binding domain (CBD) for B. cereus and the development of a highly specific and sensitive surface plasmon resonance (SPR)-based B. cereus detection method using the CBD. The newly discovered CBD from endolysin of PBC1, a B. cereus-specific bacteriophage, provides high specificity and binding capacity to B. cereus. By using the CBD-modified SPR chips, B. cereus can be detected at the range of 10(5)-10(8)CFU/ml. More importantly, the detection limit can be improved to 10(2)CFU/ml by using a subtractive inhibition assay based on the pre-incubation of B. cereus and CBDs, removal of CBD-bound B. cereus, and SPR detection of the unbound CBDs. The present study suggests that the small and genetically engineered CBDs can be promising biological probes for B. cereus. We anticipate that the CBD-based SPR-sensing methods will be useful for the sensitive, selective, and rapid detection of B. cereus.

Somatostatin cells regulate sensory response fidelity via subtractive inhibition in olfactory cortex.

Diverse types of local GABAergic interneurons shape the cortical representation of sensory information. Here we show how somatostatin-expressing interneurons (SOM cells) contribute to odor coding in mouse olfactory cortex. We find that odor-tuned SOM cells regulate principal cells through a purely subtractive operation that is independent of odor identity or intensity. This operation enhances the salience of odor-evoked activity without changing cortical odor tuning. SOM cells inhibit both principal cells and fast-spiking interneurons, indicating that subtractive inhibition reflects the interplay of multiple classes of interneurons.

Response-dependent dynamics of cell-specific inhibition in cortical networks in vivo.

In the visual cortex, inhibitory neurons alter the computations performed by target cells via combination of two fundamental operations, division and subtraction. The origins of these operations have been variously ascribed to differences in neuron classes, synapse location or receptor conductances. Here, by utilizing specific visual stimuli and single optogenetic probe pulses, we show that the function of parvalbumin-expressing and somatostatin-expressing neurons in mice in vivo is governed by the overlap of response timing between these neurons and their targets. In particular, somatostatin-expressing neurons respond at longer latencies to small visual stimuli compared with their target neurons and provide subtractive inhibition. With large visual stimuli, however, they respond at short latencies coincident with their target cells and switch to provide divisive inhibition. These results indicate that inhibition mediated by these neurons is a dynamic property of cortical circuits rather than an immutable property of neuronal classes.

El-Boustani et al. reply

replying to S.-H. Lee, A. C. Kwan & Y. Dan Nature508,http://dx.doi.org/10.1038/nature13128(2014) Several recent studies have examined the function of parvalbumin-expressing (PV+) and somatostatin-expressing (SST+) inhibitory neurons in V1 (refs 1, 2, 3). Although it is commonly agreed that these cell types alter the responses of pyramidal neurons in distinct ways—via divisive or subtractive inhibition—their specific roles remain a matter of debate. The Comment by Lee et al.4 presents new data suggesting that the differences between the results of Lee et al.2 compared to Atallah et al.3 and Wilson et al.1 could be explained by the strength and duration of laser stimulation used to optogenetically activate these two classes of inhibitory neuron. The data presented by Lee et al.4 now clarify that PV+ neurons, when probed with small amounts of optogenetic activation, do not significantly change the tuning of their target cells, confirming Atallah et al.3 and Wilson et al.1. The new SST+ results presented in the Comment4 show that SST+ neurons can subtract responses, consistent with Wilson et al.1, but we suggest that the switch of function of SST+ neurons in their data between short (1 s) and long (4–5 s) stimulation reveals a core principle of inhibition in cortical networks rather than simply being a peculiarity of stimulation protocols. The fundamental difference between these two conditions resides in the temporal overlap between inhibitory neuron activation and target-cell responses: when these overlap, inhibition is divisive (causing no change in tuning width of target neurons), but when they do not overlap, inhibition is subtractive (and reduces tuning width).

Voltage-dependent intrinsic bursting in olfactory bulb Golgi cells

In the mammalian olfactory bulb (OB), local synaptic circuits modulate the evolving pattern of activity in mitral and tufted cells following olfactory sensory stimulation. GABAergic granule cells, the most numerous interneuron subtype in this brain region, have been extensively studied. However, classic studies using Golgi staining methods identified many other, nongranule cell types in the OB whose function remains mysterious. Within just the granule cell layer (GCL), Ramón y Cajal described multiple morphologically distinct subtypes of nongranule interneurons including large spiny Blanes cells which exhibit intrinsic persistent activity. Here, we define the intrinsic electrophysiology of a different nongranule interneuronal cell type in the GCL described by Ramón y Cajal, sparsely spiny Golgi cells in the rat OB. Golgi cells exhibit two distinct firing modes depending on the membrane potential: tonic firing and bursting. Golgi cells also generate rebound bursts following the offset of hyperpolarizing steps. We find that both low-threshold burst responses to depolarizing inputs and rebound bursts are blocked by nickel, an antagonist of T-type voltage-gated Ca2+ current. The state-dependent firing behavior we report in OB Golgi cells suggests that the function of these interneurons may dynamically shift from providing rhythmic potent inhibition of postsynaptic target neurons at sniffing frequencies to tonic, subtractive inhibition based on centrifugal modulatory input.

Diagnostic evaluation of a nanobody with picomolar affinity toward the protease RgpB from Porphyromonas gingivalis

Porphyromonas gingivalis is one of the major periodontitis-causing pathogens. P. gingivalis secretes a group of proteases termed gingipains, and in this study we have used the RgpB gingipain as a biomarker for P. gingivalis. We constructed a naive camel nanobody library and used phage display to select one nanobody toward RgpB with picomolar affinity. The nanobody was used in an inhibition assay for detection of RgpB in buffer as well as in saliva. The nanobody was highly specific for RgpB given that it did not bind to the homologous gingipain HRgpA. This indicated the presence of a binding epitope within the immunoglobulin-like domain of RgpB. A subtractive inhibition assay was used to demonstrate that the nanobody could bind native RgpB in the context of intact cells. The nanobody bound exclusively to the P. gingivalis membrane-bound RgpB isoform (mt-RgpB) and to secreted soluble RgpB. Further cross-reactivity studies with P. gingivalis gingipain deletion mutants showed that the nanobody could discriminate between native RgpB and native Kgp and RgpA in complex bacterial samples. This study demonstrates that RgpB can be used as a specific biomarker for P. gingivalis detection and that the presented nanobody-based assay could supplement existing methods for P. gingivalis detection.

Increasing robustness against background noise: Visual pattern recognition by a neocognitron

The neocognitron is a hierarchical multi-layered neural network capable of robust visual pattern recognition. It has been demonstrated that recent versions of the neocognitron exhibit excellent performance for recognizing handwritten digits. When characters are written on a noisy background, however, recognition rate was not always satisfactory. To find out the causes of vulnerability to noise, this paper analyzes the behavior of feature-extracting S-cells. It then proposes the use of subtractive inhibition to S-cells from V-cells, which calculate the average of input signals to the S-cells with a root-mean-square. Together with this, several modifications have also been applied to the neocognitron. Computer simulation shows that the new neocognitron is much more robust against background noise than the conventional ones.

Subtractive inhibition assay for the detection of E. coli O157:H7 using surface plasmon resonance.

A surface plasmon resonance (SPR) immunosensor was developed for the detection of E. coli O157:H7 by means of a new subtractive inhibition assay. In the subtractive inhibition assay, E. coli O157:H7 cells and goat polyclonal antibodies for E. coli O157:H7 were incubated for a short of time, and then the E. coli O157:H7 cells which bound antibodies were removed by a stepwise centrifugation process. The remaining free unbound antibodies were detected through interaction with rabbit anti-goat IgG polyclonal antibodies immobilized on the sensor chip using a BIAcore 3000 biosensor. The results showed that the signal was inversely correlated with the concentration of E. coli O157:H7 cells in a range from 3.0 × 104 to 3.0 × 108 cfu/mL with a detection limit of 3.0 × 104 cfu/mL. Compared with direct SPR by immobilizing antibodies on the chip surface to capture the bacterial cells and ELISA for E. coli O157:H7 (detection limit: both 3.0 × 105 cfu/mL in this paper), the detection limit of subtractive inhibition assay method was reduced by one order of magnitude. The method simplifies bacterial cell detection to protein-protein interaction, which has the potential for providing a practical alternative for the monitoring of E. coli O157:H7 and other pathogens.

Label-free detection of B. anthracis spores using a surface plasmon resonance biosensor

This study demonstrates the first use of surface plasmon resonance (SPR) technology for the rapid, sensitive and label-free detection of whole B. anthracis spores. The approach involves the use of an SPR biosensor (Biacore 3000), and a monoclonal antibody which was raised against the B. anthracis spore (mAb 8G3). By means of subtractive inhibition assays, whole B. anthracis spores with concentrations as low as 10(4) colony-forming units (CFU) ml(-1) can be detected within 40 min, and other related Bacillus spores, even in high concentrations, can be differentiated from B. anthracis spores.

Gain Modulation of Neuronal Responses by Subtractive and Divisive Mechanisms of Inhibition

Gain modulation of neuronal responses is widely observed in the cerebral cortex of both anesthetized and behaving animals. Does this multiplicative effect on neuronal tuning curves require underlying multiplicative mechanisms of integration? We compare the effects of a divisive mechanism of inhibition (noisy excitatory and inhibitory synaptic inputs) with the effects of two subtractive mechanisms (shunting conductance and hyperpolarizing current) on the tuning curves of a model cortical neuron. We find that, although the effects of subtractive inhibition can appear nonlinear, they are accompanied by a change in response threshold and are best described as a vertical shift along the response axis. Increasing noisy synaptic activity divisively scales the model responses, reproducing a response-gain control effect. When mutual inhibition between subpopulations of local neurons is included, the model exhibits a gain modulation effect that is better described as input-gain control. We apply these findings to experimental data by examining how noisy synaptic input may underlie divisive surround suppression and attention-driven gain modulation of neuronal responses in the visual system.

Monoclonal antibodies for the detection of Puccinia striiformis urediniospores

The fungal pathogen Pst causes yellow rust disease in wheat plants leading to crop losses. The organism spreads by releasing wind-dispersed urediniospores from infected plants. In this study a library of novel monoclonal antibodies (mAbs) was developed against Pst urediniospores. Nine mAb-producing cell lines were cloned and their cross-reactivities characterised against a panel of airborne fungal spores representing genera commonly found in the same environment as Pst. Two specific mAbs were used to develop a competitive ELISA ( Pst mAb4) and a subtractive inhibition ELISA ( Pst mAb8). Standard curves for both assays had good intra- and interday reproducibility. The subtractive inhibition ELISA had greater sensitivity with a detection limit of 1.5 × 10 5 spores ml −1. Cross-reactivity studies of Pst mAb8 in the subtractive inhibition ELISA, showed reaction with other Puccinia spores only, suggesting that common epitopes exist within this genus. The biosensor-compatible Pst mAb8 assay principle developed in this study has the potential to be implemented in future ‘label-free’ in-the-field systems for Pst detection.